Polytetrafluoroethylene organosols and the formation of shaped articles therefrom



United States Patent POLYTETRAFLUOROETHYLENE ORGANOSOLS AND THEFORMATION OF SHAPED ARTICLES THEREFROM John Frank Lontz, Wilmington,Del., assignor to E. I. du Pont de Nemours and Company, Wilmington,Del., a corporation of Delaware No Drawing. Application October 29,1953,

Serial No. 389,160

19 Claims. (Cl. 18-54) This invention relates to new organosols based onpolytetrafluoroethylene and to methods for preparing and applying same.This application is a continuation-in-part of my copending U. S. patentapplication, S. N. 171,533, filed June 30, 1950, now forfeited.

It is well known that polytetrafiuoroethylene is highly resistant topractically all solvents and is therefore highly useful as achemically-resistant and corrosion-resistant coating and lining forvarious surfaces, containers, and the like. However, heretofore, noentirely satisfactory means have been available for readily applyingthin continuous adherent coatings of this polymer to various surfacesfrom organic media.

It is, therefore, an object of this invention to provide newcompositions based on polytetrafluoroethylene which will permit theapplication of this polymer in spinning into filaments, coating varioussurfaces, as well as in casting unsupported films. It is also an objectof this invention to provide new and useful polytetrafluoroethyleneorganosols and methods for preparing same. Other objects will beapparent from the description of the invention given below.

The above objects are fulfilled by providing a fluid organosolcomprising polytetrafluoroethylene dispersed colloidally in an organicliquid having a boiling point within the range of 30 to 200 C., saidliquid havingdissolved therein as a thickener a normally solid,substantially linear synthetic polymer which is thermally degradable andhas an average molecular weight of at least 10,000. The invention isdirected more specifically to compositions comprising by weight 5 to 50parts of colloidal particles of polytetrafiuoroethylene, which have beencoagulated from an aqueous colloidal suspension of the polymer, 95 to 50parts (complemental quantities, i. e. the total weight ofpolytetrafluoroethylene and organic liquid equals 100 parts) of an inertorganic liquid having a boiling point within the range of 30 to 200 C.,and 0.25 to 20 parts (0.25 to parts for numerous applications) of theabove thickening polymer which is thermally degradable to volatileproducts and is entirely dissolved in the said organic liquid.Preferably the thickening polymer is an elastomer selected from thegroup consisting of polymers of isobutylene, styrene, and 1,3-diolefins. More preferably the composition comprises to' parts ofcolloidal polytetrafluoroethylene as a disperse solid phase, 85 to 75parts (complementally) of a liquid hydrocarbon having a boiling point of60 C. to 150 C. as the continuous phase, and 1 to 5 parts, per 100 partsof the said polytetrafluoroethylene-liquid hydrocarbon mixture, of anisobutylene polymer or copolymer having an average molecular weight ofat least 80,000, such as polyisobutylene.

This invention also includes a preferred method of preparing theorganosols by a process which comprises intimately mixing an aqueoussuspension containing 5 to 50 parts of colloidal polytetrafluoroethylenewith 95 to 50 parts, complementally, of the inert organic liquid, and0.25 to 10 parts of the thickening polymer dissolved in said organicliquid, coagulating the polytetrafluoroethylene from the aqueous phase,and separating the aqueous phase from the resulting mixture andagitating the mixture thus obtained. The organic liquid which'isemployed as the dispersing medium is, of course, a nonsolvent forpolytetrafluoroethylene, which is, in fact, insoluble in all the commonorganic solvents, and for this reason is termed inert.

The organosol compositions of this invention may be prepared by avariety of methods. The preferred method comprises intimately mixing theorganic liquid, preferably a water-immiscible hydrocarbon, containingthe dissolved thickening polymer and an aqueous suspension of colloidalpolytetrafluoroethylene, followed by coagulation either by means ofagitation or by the addition of an electrolyte or a water-miscibleorganic liquid such as acetone or alcohol. Generally, it is preferredthat the aqueous suspension contain from 0.1 to 10%, based onpolytetrafluoroethylene content, of a dispersing agent, many examples ofwhich are disclosed in U. S. Patent 2,478,229.

An equally satisfactory method for obtaining the compositions involvescoagulating an aqueous suspension of colloidal polytetrafluoroethylene,removing the water by filtration, drying the separated coagulatedpolymer, suspending the coagulated polymer in an organic liquid mutuallyinsoluble in, or immiscible with the selected organic liquid containingthe dissolved thickening polymer, adding with continuous, rapidagitation the thickened organic liquid, whereupon the coagulated polymeris preferentially taken up by the thickened organic liquid.

A third method comprises spraying a mist of the organic liquidcontaining the dissolved viscosity-imparting polymer onto dry particlesof coagulated colloidal polytetrafluoroethylene while the particles arebeing tumbled in a closed, rotating blender.

A fourth method comprises mixing a slurry of the dry coagulatedcolloidal polytetrafluoroethylene in the organic liquid containing thedissolved thickening polymer by means of a high-speed agitator.

The organosols of this invention are mobile fluids. Pastes, dough-likematerials, etc., of restricted mobility, are not included. Theorganosols of this invention may, in certain instances, be extended ordiluted by the addition of more organic liquid. In some instances thesecompositions can be thixotropic, and extension with added liquid can beaided by mechanical treatment. They are, however, subjected tosedimentation on centrifugation.

The following examples illustrate specific embodiments of thisinvention. All parts are by weight unless otherwise specified, and allaqueous colloidal suspensions of polytetrafluoroethylene were preparedas described in U. S. Ser. No. 107,137, filed July 27, 1949, by K. L.Berry, now forfeited. The latter application discloses thepolymerization of tetrafluoroethylene at 0 to 100 C. in an aqueousmedium in the presence of a watersoluble polymerization catalyst such asdisuccinic acid peroxide, i. e. (HOOCCH2CH2OO)2, and an alkali metal orammonium salt of an acid of the formula These acids are obtainable byoxidizing, with a permanganate oxidizing agent, a polyfluoroalkanol ofthe formula H(CF2CF2)3 to ioCHzOH. The latter compounds are in turnformed by polymerization of tetrafluoroethylene in the presence ofmethanol and an organic peroxide catalyst at a temperature between C.and 350 C., as disclosed in U. S. Serial No. 65,063, filed by R. M.Joyce on December 13, 1948, now Patent No. 2,559,628.

Example 1.-An aqueous colloidal suspension of polytetrafiuoroethylenecontaining 35% polymer by weight 3 is diluted with distilled water togive an 18% polymer suspension. Two-hundred seventy-eight parts of thelatter diluted suspension (228 parts water and 50 parts polymer)containing 0.5 part of Triton N100 (a polyethylene glycol ether of analkylated phenol, which is a commercially available non-ionic dispersingagent) is mixed in a Waring Blendor with 50 parts of a commercial gradeof octane hydrocarbons containing dissolved therein 2.5 parts ofpolyisobutylene having an average molecular weight of 120,000 (VistanexB-120). This octane cut is also known as white gasoline or industrialnaphtha having a distillation range which shows 14.5% ofi at 70 C.,54.5% off at 125 C., and 90.0% oil at 180 C. After agitating at a slowspeed for 30 seconds, 200 parts acetone is added during a period of 10seconds and the entire mixture is agitated for an additional period of30 seconds. The resulting thickened, fluid organosol is separated fromthe aqueous phase by straining through a filter cloth.

Example 2.An organosol is prepared in the same manner as described inExample 1 from 25 parts of polytetrafluoroethylene in 139 parts of adilute aqueous colloidal suspension of the polymer containing 0.25 partof Triton N-100, a solution of 3.75 parts of the same polyisobutylenedissolved in 75 parts of the same commercial cut of octane hydrocarbons,and 100 parts of acetone.

The resulting fluid gel is spread on the surface of a metal plate. Onbaking at 350 0, this coating forms a tough coherent film ofpolytetrafluoroethylene.

, Example 3.An aqueous colloidal suspension of polytetrafluoroethylenecontaining 17 parts polymer, 78 parts water and 0.17 part Triton N-l isdispersed by the method of Example 1 in a Waring Blendor with a solutionof 4.4 parts of the same polyisobutylene dissolved in 83 parts of thesame cut of octane hydrocarbons, following which 68 parts acetone areadded. After the transfer of the polytetrafluoroethylene from theaqueous phase to the organic phase is complete, the upper layercontaining the organosol is decanted and centrifuged to remove occludedwater. The resulting organosol retains much of the fluidity of theaqueous colloidal suspension of polytetrafluoroethylene. This organosolis useful for spraying on metal surfaces, dry spinning into amonofilament, and for dip coating onto wire.

Example 4.-Twenty-five parts of dried, coagulatedpolytetrafluoroethylene, obtained by high speed agitation of an aqueouscolloidal suspension of the polymer, and a solution of 4 parts ofVistanex B-120 dissolved in 75 parts of industrial naphtha are mixed for3 minutes in a Waring Blendor at high speeds. The resulting gellike,fluid organosol is then removed by straining through a filtering cloth.

Example 5 .--An aqueous colloidal suspension of polytetrafluoroethylenecontaining 17 parts polymer, 78 parts water and 0085 part Triton N-100is mixed with a solution of 4.4 parts of polystyrene having an averagemolecular weight of 100,000 in 83 parts of toluene with 68 parts ofacetone in a Waring Blendor for 60 seconds. The resulting creamy fluidmixture is separated from the water phase by straining through filtercloth. The coagulated dispersion is rcdispersed with the recoveredhydrocarbon layer by an additional agitation in the Waring Blendor for 3minutes and is then suitable for use in coating and impregnatingapplications.

, Example. 6The procedure of Example 5 is repeated with the samematerials, except a solution of 4.4 parts of polymethyl methacrylatehaving an average molecular weight of 120,000 dissolved in 83 parts ofmethyl isobutyl. ketone is substituted for the polystyrene solution ofExample 5. The resulting organosol is spread on the surface of a metalstrip and then dried and baked at 350 C. to form a tough, continuous,non-porous coating of polytetrafluoroethylene.

- Example 7.--To determine the relative porosity of films Blender.

derived from granular and colloidal forms of polytetrafluoroethylene inorganic media a series of comparative tests was made, with results asset forth in the following table:

Relative porosity of films from granular and colloidal forms ofpolytetrafluoroethylene Ingredients:

25 parts polytetrafluoroethylene 71.25 parts of organic liquid 3.75parts of thickening polymer Porosity (cc. air/ min/sq. ern./milthickness) Film Thickness (mils) Polytetrafluoroethylene Form ThickeningPolymer Organic Liquid Granular* Polystyrene D0* do Colloidal do doGrauular* Polymethyl meth- Methyl isoacrylate. bu tyl ketone. D o* do doColloidal do do *Mieropulverized product.

The films were prepared by spreading out the dispersions on a flat paperby means of a spatula with enough pressure, particularly with thegranular preparation, to produce an even texture. After drying a fewminutes the film was then stripped off and baked at 350 C. for 30minutes. The porosity was measured by applying a stream of air at astatic pressure of l-inch of mercury through a test coil having a/2-inch circular opening in which the film is inserted. The air flowrate at approximately room temperature (25 C.) was determined by meansof a Wet test meter using timed intervals for measured volumes of airthrough-put. The porosity was then calculated as the cubic centimetersof air per minute that passed through a square centimeter of area permil thickness. On a quantitative basis, it was evident from the abovethat the relative porosity of the granular polymer film was of the order20 to 32 times greater than that of the colloidal polymer film.Furthermore, examination of the test pieces showed that the tWo types offilms were structurally different: the granular form Was opaque and toreeasily with a fibrous appearance, whereas, the colloidal form wastransparent and had a higher tear strength with no fibrous appearancebut With practically complete interparticle fusion.

Example 8.-A dispersion containing 25 grams of poly tetrafluoroethylenein 40 grams of Water was admixed with a solution of 13 grams ofpolybutylene in grams of Skellysolve E (petroleum fraction) in a WaringTo the resulting mixture was added 10 grams of aqueous 14% hydrochloricacid, and the Water which separated was removed from the compositionthus obtained. After removal of the water, the mixture was extruded intowarm air to produce a filament which was thereafter sintered at 400 C.Upon being cold-drawn (4X), the fiber had a tenacity of 0.6 gram/denier(50% elongation), and a modulus of 2 grams/ denier.

The polytetrafluoroethylene filaments, prepared in accordance with thepresent invention, have excellent strength, and are highly useful innumerous applications. When the filaments are spun by extrusion througha die having a diameter of 0.007 inch, followed by passage of the fiberthrough a heated zone at a temperature high enough to evaporate thefluid, suitably above the boiling point of the fluid medium, and passagethrough a sintering oven at a temperature above the 327 C. transitiontemperature to consolidate the polytetrafluoroethylene to maximumstrength (for the undrawn fiber), filaments having strengths of, forexample, 4000 to 16000 p. s. i. are produced. Filaments as hereinaboveillustrated, can

' be drawn at room temperature to obtain filaments of higher tensilestrength; in some instances, such-filaments canbe drawn at a drawratio-as high at 10:1.

The polytetrafluoroethylene for use in this invention may be obtained bycoagulating an aqueous colloidal suspension of the polymer. Otherfinely-divided forms of polytetrafiuoroethylene, such as the granularform obtained by direct polymerization in accordance with U. S. Patents2,230,654, 2,393,967, and 2,394,243, the mircopulverized form, or anyother form which has been mechanically subdivided from the massivepolymer cannot be used to form the organosols of this invention. Theprocess of preparing the aqueous suspension of the polymer is not thesubject of this invention. However, suitable aqueous suspensions may beobtained by the methods described in U. S. Ser. No. 713,385, filedNovember 30, 1946, by M. M. Renfrew, now Patent No. 2,534,058; U. S.Ser. No. 107,137, filed July 27, 1949, by K. L. Berry; and U. S. Patent2,478,229. The particle size of the polymer appears to be somewhatcritical; i. e., the particles should be of colloidal size beforecoagulation, and the smaller the particles the more satisfactory are-theorganosols. The particle size of the polymer in the suspensionsdescribed in the above-mentioned applications and patent in generalranges from 0.05 to 5 microns, which is the diameter of the averageparticle determined by an electron microscope measurement on a driedfilm obtained by depositing a highly diluted aqueous suspension ofpolytetrafluoroethylene on a surface. These colloidal suspensions havebeen found quite suitable for coagulation in preparing the organosols ofthis invention. After coagulation of the aqueous suspension, theparticles of polytetrafluoroethylene may tend to agglomerate somewhat,but this does not prevent the polytetrafiuoroethylene from dispersing inorganic liquids containing the thickening polymer to yield organosols.

The preferred organic liquids are the hydrocarbons having a boilingpoint of 60 C. to 150 C. at atmospheric pressure. The lower boilinghydrocarbons are preferred since they provide an organosol from whichthe liquid hydrocarbon may be rapidly evaporated. The liquid hydrocarbonmay be aliphatic, cycloaliphatic, or aromatic, and may be eithersaturated or unsaturated, although the preferred hydrocrbons are thesaturated aliphatic hydrocarbons. Examples of specific hydrocarbonswhich are suitable include hexane, heptane, octane, nonane, decane,diisobutylenes, heptene, octene, cyclohexane, benzene, toluene, xylenes,mesitylene, hemimellitene, ethylbenzene, propylbenzne, terpenes, andcommercial mixtures of various hydrocarbons, such as mixtures ofaliphatic and aromatic hydrocarbons, and mixtures of saturated andunsaturated hydrocarbons.

The organic liquid is not limited to the preferred hydrocarbons, sinceany suitable inert organic liquid or mixture of liquids having a boilingpoint less than 200 C. at atmospheric pressure is suitable for use inthe present invention. In some cases commercial mixtures ofimpureorganic liquids may contain small fractions boiling close to orslightly above 200 C., but the major portion should boil well below 200C., and in general the boiling point will be from 30 C. to 200 C. Thechoice of liquids other than the preferred hydrocarbons depends on thechoice of thickening polymer as well as the volatility and evaporationrate desired in the final organosol composition. Suitable liquidsinclude ketones, esters, and ethers, specific examples of which aremethyl isobutyl ketone, mesityl. oxide, amyl acetate, n-butyl acetate,and n-butyl lactate.

The amount of organic liquid in the organosol must be sufficient toprovide a liquid composition which can be readily used for coating byspraying, dipping, and other conventional methods. On the other hand,there must be sufficient polytetrafluoroethylene in the organosol toprovide thick enough coats in'one application, where desired. Hence, theamount of organic liquid in the organosol may vary between 95 and 50parts by weight and the amount of coagulated colloidalpolytetrafluoroethylene may vary from 5 to 50 parts by weight, providedthat the sum of the two weights is 100 parts. The-preferred ranges areto 75 parts organic liquid, preferably hydrocarbon, and 15 to 25 partspolytetrafluoroethylene.

The role of the viscosity-imparting polymer (i. e. thickening polymer)in the organosol is important for two reasons. First, it acts as athickener for the organic liquid, thereby facilitating the applicationof the composition to surfaces by conventional methods. The thickeneralso prevents excessive agglomeration of the colloidalpolytetrafluoroethylene particles during the coagulation step intransferring the polytetrafluoroethylene from the aqueous phase to theorganic phase in the preparation of the organosol. Secondly, the polymeris important in coating, casting, and spinning applications in that itserves to bind the polytetrafiuoroethylene sol after the organic liquidhas been removed from the polytetrafiuoroethylene article, whereby, uponsubsequent sintering, high quality polytetrafluoroethylene films,fibers, etc., are formed. This second function of the thickening polymeris quite critical, especially in casting thin films and in providingthin coatings of reproducible thickness and low vapor permeability. Inthis respect a greater problem was encountered when it was attempted toprepare satisfactory thin coatings and cast films from a mixture offinely divided comminuted or micropulverized polytetrafluoroethylene (i.e., not polymer of colloidal size such as is obtained by coagulation ofan aqueous colloidal suspension) dispersed in an organic liquid mediuscontaining a dissolved polymeric thickener. These mixtures invariablyyield relatively porous coatings and films which, although useful forcertain applications, are completely unsatisfactory for some of the moreimportant electrical insulating and chemical resisting applications forpolytetrafluoroethylene. Hence, in order to provide satisfactoryorganosols in accordance with this invention, polytetrafluoroethyleneparticles of colloidal size, must be used and also-a viscosity-impartingpolymer, which is thermally degradable and which has an averagemolecular weight of at least 10,000, must be used. Moreover, the saidviscosity-imparting polymer in the preferred compostions of thisinvention should preferably be completely soluble in the amount oforganic liquid employed in the particular organosol composition. Theproportion of the viscosityimparting polymer may vary from 0.25 to 20parts (0.25 to 10 parts for many applications) by weight, based on partsby weight of the combined organic liquid and polytetrafluoroethylenepresent in the organosol. It is preferred to use an isobutylene polymer(which includes copolymers) having an average molecular weight of atleast 80,000. The preferred group of viscosity-imparting polymers areelastomers (i. e. those polymers and copolymers having rubberyproperties); these include polyisobutylene, isobutylene/ styrenecopolymers, isobutylene/ diolefin copolymers i. e., the butyl rubbers),styrene/diolefin copolymers, diolefin/acrylonitrile copolymers, andpolychloroprene. Other suitable polymers which are thermally degradableto volatile products and satisfy the other requirements are polystyrene,polymethyl methacrylate, and polyvinyl acetate. These degradablethickeners are addition polymers, as distinguished from condensationpolymers, or other polymers which do not behave as herein described,when heated. Polymers such as polyvinylidene compounds (polyisobutylene,.polymethyl methacrylate, polybutyl methacrylate, etc.), which can bedecomposed thermally into the monomers from which they are derived,suitably at 250 to 500 C., are especially useful as thickeners.

Small amounts of other materials may be incorporated in the compositionsof this invention depending upon the properties desired in the finishedarticles fabricated from the compositions. Thus, there may be added tothe compositions, either during the formation of the organosol or afterthe preparation of the organosol, finely divided solid fillers,pigments, dyes, lubricants, plasticizers, dispersing agents,stabilizers, and the like.

The chief advantage of this invention is that it permits the applicationat room temperature and slightly elevated temperatures of thin coatingsof polytetrafluoroethylene as wellas the casting of thin films andformation of filaments of polytetrafluoroethylene rapidly andeconomically. Another advantage is that the organosols may be used toimpregnate porous structures such as paper, cloth, asbestos, and thelike, the most important advantage being that the organosol is in a formwhich will not aifect the water-sensitive structures such as occurs whenapplying an aqueous suspension of polytetrafiuoroethylene. Theorganosols also permit the coating of iron and steel surfaces whichpresent a corrosion problem when coating with an aqueous suspension ofpolytetrafluoroethylene. Coatings and films prepared from the organosolsdry more rapidly than those from aqueous suspensions ofpolytetrafluoroethylene.

In most applications employing the organosols, the organic liquid willbe removed by conventional methods leaving the polytetrafiuoroethyleneparticles bound together by the thickening polymer. The structure isthen heated to a temperature of 250 C.500 C. until the thickeningpolymer is completely degraded, and the heating is continued above 327C. until the polytetrafiuoroethylene becomes sintered into smooth,coherent, continuous, non-porous films, coatings, or filaments, whichpossess a high degree of chemical resistance and excellent electricalinsulating properties. The polymers employed as thickeners arepreferably those which degrade to volatile products when heated at 250C. to 500 C. without causing charring or discoloration or withoutaflecting the inherently good electrical properties of thepolytetrafluoroethylene; other organic thickening polymers such ascellulose derivatives have been found unsatisfactory as substitutes forthe particular group of normally solid, substantially linear syntheticpolymers defined herein. The elastomers which are generally degraded tomonomer components upon heating to a temperature of 300 to 350 C., arepreferred because they yield more flexible and more strongly-coherentcoatings, filaments, and films prior to sintering thepolytetrafluoroethylene. Printing with pigmented organosols foridentification purposes or for decorative effects may be readily appliedto bake, sintered polytetrafluoroethylene surfaces using conventionalprinting rolls or screens, followered by baking above 327 C. (preferably327 to 500 C. to fuse the pigmented application.

The most important uses for the organosol compositions include spinningfilaments and casting films, dipcoating wires, spray-coating metalsurfaces, impregnation of water-sensitive materials such as asbestos,and, in fact, any other coating, impregnating, casting, or sprayingapplications.

I'claim:

' '1. A process for preparing a fluid organosol which comprisesintimately mixing an aqueous suspension containing to 50 parts by weightof colloidal polytetrafluoroethylene with 95 to 50 parts,complementally, of

an inert organic liquid which is a non-solvent for thepolytetrafluoroethylene, said organic liquid having dissolved thereinfrom 0.25 to 10' parts of a normally solid, substantially linearsynthetic addition polymer which is thermally degradable into volatileproducts at 250 to 500 C. and has an average molecular weight of atleast "10,000, coagulating the polytetrafluoroethylene from the aqueousphase, separating the aqueous phase from the resulting mixture andagitating the mixture thus obtained whereby an organosol which iseffective as a coating composition. for applying polytetrafluoroethylenecoatings to surfaces is obtained.

' 2. A fluid organosol comprising as a disperse solid phase from 5' to50 parts by weight of colloidal polytetrafluoroethyl'ene, and as acontinuous phase from 95 to parts, complementally, of an inert organicliquid which is a non-solvent for the said polytetrafluoroethylene, per100 parts of said organosol, said liquid having a boiling point withinthe range of 30 to 200 C., said liquid having dissolved therein from0.25 to 10 parts of a normally solid, substantially linear syntheticaddition polymer which is thermally degradable into volatile products ata temperature of 250 to 500 C., the average molecular weight of the saidaddition polymer being at least 10,000.

3. The process which comprises extruding the composition of claim 2 inthe form of a filament, evaporating said inert organic liquid therefrom,and compacting the resultant filament at a temperature sufliciently highto sinter the polytetrafluoroethylene.

4. The process which comprises forming a film of polytetrafluoroethyleneby evaporation of said inert liquid from a film of the organosol definedby claim 2, and heating the resulting film until the said additionpolymer has been removed by thermal degradation to volatile products.

5. A fluid organosol comprising as a disperse solid phase from 15 to 25parts by weight of colloidal particles of polytetrafiuoroethylene and asa continuous phase from 85 to 75 parts, complementally, of an inertorganic liquid which is a non-solvent for the saidpolytetrafluoroethylene, said liquid having a boiling point in the rangeof to 150 C., said liquid having dissolved therein from 1 to 5 parts ofan isobutylene polymer, the average molecular weight of the saidisobutylene polymer being at least 80,000.

6. The composition of claim 5 in organic liquid is a hydrocarbon.

7. The composition of claim 5 in organic liquid is octane.

8. The composition of claim 5 in organic liquid is methyl isobutylketone.

9. The composition of claim 5 in which the said which the said which thesaid which the said organosol contains a dispersing agent.

10. The composition of claim 9 in which the said dispersing agent is apolyethylene glycol ether of an alkylated phenol.

11. A process for preparing a fluid organosol which comprises intimatelymixing an aqueous suspension containing 15 to 25 parts by weight ofcolloidal polytetrafluoroethylene with 85 to parts, complementally, of avolatile inert organic liquid which is a non-solvent for thepolytetrafluoroethylene, said organic liquid having dissolved thereinfrom 1 to 5- parts of a normally solid, substantially linear syntheticpolymer of the class consisting of polyisobutylene, polystyrene, andpolymethyl methacrylate, said synthetic polymer being one which isthermally degradable into monomer components at 250 to 500 C. and has anaverage molecular weight of. at least 10,000, coagulating thepolytetrafluoroethylene from the aqueous phase, separating the aqueousphase from the resulting mixture and agitating the mixture thus obtainedwhereby an organosol which is etfective as a coating composition forapplying polytetrafluoroethylene coatings to surfaces is obtained.

12. The process of claim 11 in which the said organic liquid is an inerthydrocarbon.

13. The process of claim 11 in which the said organic liquid is octane.

14. The process of claim 11 in which the said organic liquid is methylisobutyl ketone.

15. The process of claim 11 in which the said aqueous suspensioncontains from 0.1 to 10%, based on'the weight ofpolytetrafluoroethylene, of a dispersing agent.

16. The process of claim 15 in which the said dispersing agent is apolyethylene glycol ether of an alkylated phenol.

17. The process of claim. 15 in which the said dissolved vinylidenepolymer is polyisobutylene having an average molecular weight of atleast 80,000.

18. A process for preparing a fluid organosol containing colloidalpolytetrafiuoroethylene dispersed in an inert organic liquid having aboiling point Within the range of 30 to 200 C., said liquid havingdissolved therein as a thickener a normally solid, substantially linearsynthetic polymer of the class consisting of polyisobutylene,polystyrene, and polymethyl methacrylate, said synthetic polymer beingone which is thermally degradable at 250 to 500 C. into the monomersfrom which it is derived and has an average molecular weight of at least10,000, which comprises coagulating polytetrafiuoroethylene from anaqueous colloidal suspension thereof, drying the coagulatedpolytetrafiuoroethylene, forming a slurry of the dry, coagulatedpolytetrafiuoroethylene, in the said organic liquid containing thedissolved thickener and subjecting the resulting mixture to the actionof high-speed agitation, whereby an organosol which is efiective as acoating composition for applying polytetrafiuoroethylene to surfaces isobtained.

19. The process of claim 18 in which the said thickener ispolyisobutylene having an average molecular weight of at least 80,000.

References Cited in the file of this patent UNITED STATES PATENTS2,393,967 Brubaker Feb. 5, 1946 2,413,498 Hill Dec. 31, 1946 2,456,255Coffman Dec. 14, 1948

2. A FLUID ORGANOSOL COMPRISING AS A DISPERSE SOLID PHASE FROM 5 TO 50PARTS BY WEIGHT OF COLLOIDAL POLYTETRAFLUOROETHYLENE, AND AS ACONTINUOUS PHASE FROM 95 TO 50 PARTS, COMPLEMENTALLY, OF AN INERTORGANIC LIQUID WHICH IS A NON-SOLVENT FOR THE SAIDPOLYTETRAFLUOROETHYLENE, PER 100 PARTS OF SAID ORGANOSOL, SAID LIQUIDHAVING A BOILING POINT WITHIN THE RANGE OF 30* TO 200* C., SAID LIQUIDHAVING DISSOLVED THEREIN FROM 0.25 TO 10 PARTS OF A NORMALLY SOLID,SUBSTANTIALLY LINEAR SYNTHETIC ADDITION POLYMER WHICH IS THERMALLYDEGRADABLE INTO VOLATILE PRODUCTS AT A TEMPERATURE OF 250* TO 500* C.,THE AVERAGE MOLECULAR WEIGHT OF THE SAID ADDITION POLYMER BEING AT LEAST10,000.
 3. THE PROCESS WHICH COMPRISES EXTRUDING THE COMPOSITION OFCLAIM 2 IN THE FORM OF A FILAMENT, EVAPORATING SAID INERT ORGANIC LIQUIDTHEREFROM, AND COMPACTING THE RESULTANT FILAMENT AT A TEMPERATURESUFFICIENTLY HIGH TO SINTER THE POLYTETRAFLUOROETHYLENE.